1) Field of the Invention
The invention herein relates to measuring hardware, specifically a tape rule with an automatic blade extension mechanism in which the torsion developed by winding the steel ruler blade around the reel is of sufficient magnitude such that when the ruler blade is released, it automatically extends. At the same time, the present invention is equipped with a gear train that enables the smooth retraction of the ruler blade to thereby further enhance the practical value of tape rule herein.
2) Description of the Prior Art
A conventional tape rule is comprised of a tape reel that consists of a center-wound, spiral spring at the interior section, a ruler blade wound on the exterior section, and a hook riveted to the front end of the ruler blade; the center section of the spiral spring on the said tape reel is inserted over the center shaft of the left case half; and the front end of the ruler blade is positioned in a bumper block which is secured inside the bottom section and front end of the left case half, with the other side of the said bumper block secured inside the bottom section and front end of the right case half; and a plurality of screws are inserted through the right case half and fastened into the center shaft and mounting posts of the left case half to thereby complete the assembly of the tape rule body. The conventional product is utilized by pulling out the ruler blade of the tape rule to an appropriate length during a measurement operation and then releasing the hook of the tape rule when measuring is finished. Since the tension of the spiral spring (similar to the type utilized in most tape rule spring mechanisms) inside increases in proportion to the length unwound and, therefore, the rewinding speed is faster when the length is greater; if the said ruler blade is constructed of metal, the user is susceptible to cutaneous injuries of the hand, which is an inconvenient shortcoming of the conventional product. Furthermore, if the rewinding speed is too rapid, the force of impact against the bumper block is intensified, the poor cushioning performance by the conventional bumper block often leads to the dislodging of the hook, a serious shortcoming that preludes further utilization. In the structure of the said conventional tape rule a spiral spring is installed in the tape rule to enable the forceful retraction of the ruler blade when the ruler blade hook is released after measurement is completed. Conversely, when the user wants to perform a measurement, the ruler blade must be pulled from the tape rule to an appropriate length, but such an operation is extremely inconvenient if done as a one-man operation. To innovate a more practical and convenient tape rule, the inventor of the invention herein conducted exhaustive research and development based on many years of professional manufacturing experience and, furthermore, subjected the results to extensive testing and further refinement to achieve an even higher level of practical value, which finally culminated in the tape rule with an automatic blade extension mechanism.
Therefore, the primary objective of the invention herein is to provide a tape rule with an automatic blade extension mechanism, wherein the torsion developed by winding the steel ruler blade around the reel is of sufficient magnitude such that when the ruler blade is released, it automatically extends and, furthermore, a rewinding gear train is built-in, thereby further improving the tape rule structure and increasing its practical value.
To enable the examination committee a further understanding of the structural features and content as well as the advantages and features of the present invention, the brief description of the drawings below are followed by the detailed description of the invention.